1. Field of the Invention
The present invention relates to an image display apparatus configured to display an image by utilizing light modulated by an image display element, and more particularly to the image display apparatus configured to illuminate the image display element by utilizing light beams from a plurality of light sources.
2. Description of the Related Art
An image display apparatus, such as a liquid crystal projector (image projection apparatus) often utilizes, as a light source, a discharge lamp such as a high-pressure mercury lamp or a xenon lamp. However, in the discharge lamp, as wattage increases an arc length increases, and as an arc length increases the light quantity used to illuminate the image display element decreases among a light emission amount from the discharge lamp or the light utilization efficiency decreases. Therefore, if only a single discharge lamp is used, there is a limit in improving the light utilization efficiency and in obtaining a brighter projected image.
Accordingly, Japanese Patent Laid-Open No. 2001-264697 discloses an image projection apparatus that uses a plurality of light sources or is configured as a multi-light type so as to increase the light quantity used to illuminate the image display element and to project a brighter image. This image projection apparatus converts light beams from two light sources into P-polarized light and S-polarized light respectively through two polarization conversion elements, combines the P-polarized light and S-polarized light with each other by using a polarization beam splitter (“PBS”), converts the combined light into P-polarized light or S-polarized light through another polarization conversion element, and introduces the converted light to the image display element.
The polarization conversion element in combination with an integrator system can provide high polarization conversion efficiency. Therefore, the image projection apparatus disclosed by Japanese Patent Laid-Open No. 2001-264697 arranges two polarization conversion elements and two integrator systems in an optical path from each light source to the image display element.
However, the light utilization efficiency (illumination efficiency) remarkably lowers as a result of that the two integrator systems are arranged in the optical path from the light source to the image display element. Hence, it is difficult to obtain sufficiently high illumination efficiency in the image projection apparatus disclosed by Japanese Patent Laid-Open No. 2001-264697.